A wide variety of mental and physical processes are controlled or influenced by neural activity in particular regions of the brain. In some areas of the brain, such as in the sensory or motor cortices, the organization of the brain resembles a map of the human body; this is referred to as the “somatotopic organization of the brain.” Several areas of the brain appear to have distinct functions that are located in specific regions of the brain in most individuals. For example, areas of the occipital lobes relate to vision, regions of the left inferior frontal lobes relate to language in the majority of people, and particular regions of the cerebral cortex appear to be consistently involved with conscious awareness, memory, and intellect. This type of location-specific functional organization of the brain, in which discrete locations of the brain are statistically likely to control particular mental or physical functions in normal individuals, is herein referred to as the “functional organization of the brain.”
Many problems or abnormalities with body functions can be caused by damage, disease and/or disorders of the brain. A stroke, for example, is one very common condition that damages the brain. Strokes are generally caused by emboli (e.g., vessel obstructions), hemorrhages (e.g., vessel ruptures), or thrombi (e.g., clotting) in the vascular system of a specific region of the cortex, which in turn generally causes a loss or impairment of a neural function (e.g., neural functions related to face muscles, limbs, speech, etc.). Stroke patients are typically treated using physical therapy to rehabilitate the loss of function of a limb or another affected body part. For most patients, little can be done to improve the function of the affected limb beyond the recovery that occurs naturally without intervention.
One existing physical therapy technique for treating stroke patients constrains or restrains the use of a working body part of the patient to force the patient to use the affected body part. For example, the loss of use of a limb is treated by restraining the other limb. Although this type of physical therapy has shown some experimental efficacy, it is expensive, time-consuming and little-used. Stroke patients can also be treated using physical therapy and/or drug therapies. For example, some types of drugs, including amphetamines, increase the activation of neurons in general. However, these drugs may have limited efficacy because the mechanisms by which they act are very non-selective, and because they cannot be delivered in appropriate concentrations directly at the site where they are needed. Still another approach is to apply electrical stimulation to the brain to promote the recovery of functionality lost as a result of a stroke. Typically, electrical stimulation is applied at or near the damaged tissue, or at homologous tissue located in the brain hemisphere opposite the hemisphere at which the neural damage has occurred (i.e., the contralesional hemisphere). While this approach has been generally effective, in some cases such stimulation may not improve functionality to the desired and/or expected degree. Therefore, there is a need to develop more effective and efficient treatments for rehabilitating stroke patients and patients who have other types of neurologic dysfunction or damage.